Review Question - QID 210269

This player has sustained a tear of the medial collateral ligament (MCL). The MCL is a ligament which inserts indirectly into bone through Sharpey's fibers.

Ligaments can insert on bone either indirectly and directly. Indirect is the most common and is a fibrous insertion. The superficial fibers of the tendon insert into the periosteum, while the deep fibers insert directly into the bone. These deep fibers are called Sharpey's fibers and are made of type I collagen. The direct insertion has both deep and superficial fiber insertions as well. Direct insertions are fibrocartilaginous and consist of four transitional zones of increasing stiffness that allow force dissipation.

Lu et al. performed a review to determine the functional attachments of soft tissue to bone. They report that a specialized interface, called an insertion site or enthesis, integrates tendon or ligament to bone and serves to facilitate joint motion. Fibrous (indirect) insertions typically occur over large areas, presumably to distribute force and reduce stress, and are characterized by perforating mineralized collagen fibers.

Cole et al. performed a review of fixation of soft tissues to bone. They report that recreation of the enthesis relies on adequate biologic healing afforded by adequate initial fixation. The healing pattern associated with direct soft–tissue-to-bone repair, such as rotator cuff repair, is different from that associated with fixation within bone tunnels (ex. ACL reconstruction). The process of tendon healing within osseous tunnels occurs over time.

Lui et al. performed a review of the biology and augmentation of tendon-bone insertion repair. They report that when a ligament runs parallel to the bone, like the MCL, the insertion is more likely to be indirect. When a ligament enters the bone perpendicularly, such as the ACL, the insertion is direct. Indirect insertions may be elevated off the bone without cutting the ligament itself while direct insertions require cutting the substance of the ligament to detach it.

Figure A is a T2-weighted, coronal MRI demonstrating a tear of the MCL. Illustration A is a polarized photomicrograph demonstrating Sharpey fibers, indicated by the white arrows. G represents tendon, while B represents bone (Liu et al.). Illustration B is a Safranin-O-staining photomicrograph of a direct tendon insertion site (Liu et al.). Illustration C is an H&E photomicrograph of the same direct tendon insertion site (Liu et al.). B represents bone, CFC represents calcified fibrocartilage, UCFC represents uncalcified fibrocartilage, and T represents tendon.

Incorrect Answers:
Answers 1, 2, 3, & 5: The MCL is a ligament which inserts indirectly into bone through Sharpey's fibers.